a)nuclear processes have a very high activeation energy becasue of the electric repulseion of the protons.
b)helium nuclei have twice the carge of protons so repel even more strongly, making the activation renergy higher
c)mass of reactants=3*4.001506=12.004518u
mass of product=12u
difference=0.004518u
mass=0.004518*1.57*10^-27kg
E=mc^2=0.004518*1.57*10^-27*(3*10^8)^2=6,79*10^-13J